The overall objective of this project is to exploit the transgenic mouse system by introducing natural or manipulated gene sequences into the germ line of an animal and to alter its phenotype and genetic background. This system provides a new way of investigating tissue-specific and developmental stage-specific regulation of gene expression. The current research is focused on two classes of genes that may be associated, initially, with the multistage process of murine liver tumorigenesis: (1) the known oncogenes, myc, ras and SV40 T antigen, and (2) the developmental expression of a family of genes that contain sequences homologous to the Drosophila homeobox. Work in the past year has focused on setting up the transgenic mouse system and on cloning putative murine homeotic genes. We have succeeded in making transgenic mice following micro-injection of SV40 T antigen under the control of the metallothionin promoter. The genomic localization and expression of the introduced sequences are being characterized. Other oncogene constructs are currently being employed to obtain new transgenic mice lines. We have also obtained six independent, putative homeotic clones from a rat genomic library. DNA sequence analysis indicates these clones contain sequences exhibiting greater than 90% homology to the consensus homeobox sequence. We have observed expression of these genes in spinal cord, brain and embryo.